Wow, so I have a little piece of Mac history then! Awesome. Anyone know what's the newest OS X it can run?That is one of the last PowerMac G4s that were made. Known as the Mirror Drive Door or MDD. There were 3 variations released in 2002-3. The monitor is one of the early Cinema displays. Probably from the same time as the MDD.
That is Leopard:https://en.wikipedia.org/wiki/Mac_OS_X_LeopardThe newest version of OS X it can run is 10.5.8.